Speaker: Carlos Paz-Soldan, General Atomics
Title: The Measurement and Control of Relativistic Electrons in Tokamaks
Abstract: Rapid plasma shutdowns in the tokamak fusion reactor configuration have the potential to generate intense beams of relativistic (multi-MeV) electrons that pose a severe risk to the integrity of plasma-facing components. Demonstrating control of these MeV populations will be among the first research challenges to overcome on the path to achieving the net fusion energy mission of the ITER tokamak, currently under construction in France. Insight into the dynamics of the relativistic electrons is gained by measuring their volumetric emission via either the bremsstrahlung or synchrotron mechanisms. A new imaging diagnostic has recently been deployed in the DIII-D tokamak to measure bremsstrahlung-emitted MeV photons. Capable of separating real space from phase space effects, these measurements are providing unique stress-tests for theoretical models. Deficiencies in specific areas of phase space point to interactions with kinetic instabilities (driven by the electrons themselves) as an important, yet previously ignored, mechanism governing the electron behavior. Experiments have directly observed the kinetic instabilities for the first time, confirming predictions and opening new pathways for control. This seminar will describe the development of these novel measurements, their interaction with improving theoretical models, and finally discuss ongoing activities to harness instability effects for control applications.
Biography: Dr. Carlos Paz-Soldan is a Scientist with the DIII-D National Fusion Program at General Atomics, in San Diego, California. Dr. Paz-Soldan received his PhD from the University of Wisconsin-Madison in 2012. His doctoral research concerned observations of enhanced plasma stability with high-speed differentially rotating conducting walls. For this work he was awarded the Marshall N. Rosenbluth Outstanding Doctoral Thesis Award by the American Physical Society. Dr. Paz-Soldan’s present research focuses on the control of transient events in tokamaks, and he maintains efforts in several aspects of this problem. Since 2016, Dr. Paz-Soldan has been leading the DIII-D edge-localized mode (ELM) control research area. His own work in this area focuses on the development of ELM-controlled tokamak scenarios and optimizing non-axisymmetric (3D) magnetic field configurations for transient control. He is leading the development of next-generation 3D electromagnets for the DIII-D research program and beyond. Dr. Paz-Soldan is also very active in understanding how to control energetic electron populations accelerated after a tokamak disruption. His work in this area focuses on measuring the dynamics of these relativistic particles both for benchmarking theoretical models as well as to develop novel means for their control, as he will describe in this seminar.